It did not give further details of the drone ship, but mainland military watchers posted on social media that the images looked similar to the Wave Glider – an autonomous boat that is wave- and solar-powered, built by US company Liquid Robotics, a Boeing subsidiary.

Song Zhongping, a Hong Kong-based military commentator and former People’s Liberation Army instructor, said underwater vehicles were often used to gather oceanographic data – including on salinity, sea flow, water temperature and sound speed – that could be used in anti-submarine warfare.

“Anti-submarine warfare requires a lot of basic information … [including] background noise signals,” he said.

Song said the United States military had deployed a “large number” of drones in waters near China to keep its database “updated” so that it could detect and monitor Chinese submarines.

“These vehicles can be identified via GPS and they can transfer information via satellite, which makes them more efficient [in collecting information] and a great threat to China’s national security,” he said.

According to the state television report, fishermen are increasingly finding suspected surveillance drones in waters off China’s eastern and southern coasts – the government now offers a reward to anyone who reports a suspicious device.

Tang Jiansheng, a researcher with the unnamed institute, told CCTV that the recently discovered drone ship could receive instructions in real time and it was equipped with “many sensors that enabled it to acquire a large amount of ocean environment data”.

“The three solar panels were supporting those sensors so it could have been working for a long time, continuously collecting data on the marine environment in the waters around China,” he said.

“If it knew the environment well, it put the concealment of our underwater targets at risk.”